module event_type();

// Declare a new event called ack
event ack; 
// Declare done as alias to ack 
event done = ack; 
// Event variable with no synchronization object
event empty = null; 

initial begin
    #1 -> ack;
    #1 -> empty;
    #1 -> done;
    #1 $finish;
end

always @ (ack) begin
    $display("@ %g: ack event emitted", $time);
end

always @ (done) begin
    $display("@ %g: done event emitted", $time);
end

endmodule
